The requirement that Newton's laws be the limit of general relativity for small v forces lambda to be very small. Setting it equal to zero gives all the correct predictions for the motions of planets to within measurable accuracy. Put another way, if 0, then experimental data shows that it must be very small indeed. Also, we could take that term over to the right-hand side of the equation and incorporate it into the stress-energy tensor, thus regarding -gab/8 as the stress-energy tensor of empty space.

Following is an excerpt from an article in Scientific American (September, 1996, p. 22):

 

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